Assessment of Hydro-climatic Variables and Its Impact on River Flow Regime in the Sub-basins of the Upper Indus Basin

The assessment of hydro-climatic variables plays a key role to examine long-term changes in snow-fed and glacier-fed rivers that are vulnerable to climatic variations in areas of complex topography. This study investigated monthly, annual and seasonal variability of three major elements in the water system, temperature, precipitation and streamflow changes to determine their relationships, using Terra climate, a high-resolution regional climate modeling product and in situ river discharge data in the Upper Indus Basin (UIB). Long-term (1960-2017) trends and magnitudinal changes in hydro-climatic variables were determined by applying modified Mann-Kendall and Sen's slope test. The spatial variations in climate variables show significant trends that are strongly regulated by the altitude. Overall, warming trends are greater in spring and higher with elevation. The temperature trends show significant increase in maximum temperature (Tmax) during autumn (0.09 degrees C/decade), spring (0.22 degrees C/decade) and winter (0.12 degrees C/decade), while decrease in summer (- 0.07 degrees C/decade). A significant decrease in Tmax was observed in the Hunza and Jhelum sub-basins which indicate a suspected pattern of summer cooling over the period. Tmax exhibited large spatio-temporal variations with respect to high (e.g., Hunza and Shyok) and low (e.g., Jhelum and Kabul) altitude sub-basins, in contrast to more homogenous patterns of trends in minimum temperature (Tmin) across the whole UIB. River discharge from high-altitude sub-basins was positively correlated with temperature, while in low-altitude sub-basins with precipitation. A clear trend in annual and seasonal variations in hydro-climatic variables from the snow-fed and glacier-fed sub-basins could be a response to climatic factors.